Method of purifying exhaust gases



Feb. 23, 1965 D. HONERKAMP 3,170,758

METHOD 0F PURIFYING EXHAUST GASES Filed Sept. 1, 1960 Z 0 9 N 5: I 5 L) c S 2 g M E 3 2 rc D 3' 3: 5

g u. E '5 3 INVENTOR DONALD L,HONERKAMP a gamma/ CM ATTORNEYS United States Patent Office 3 170 75s smrnon or PURll YllWG EXHAUST GASES Donald L. Honerkamp, Tinley Park, 111., assignor, by

mesne assignments, to Sinclair Research, Inc., New- York, N.Y., a corporation of Delaware Filed Sept. 1, 1960, Ser. No. 53,503 2 Claims. (Cl. 232) This invention relates to a method for purifying exhaust gases, particularly exhaust gases from internal combustion engines. The chief constituents on a volumetric basis of the exhaust gases of conventional gasoline and diesel engines, for example, are nitrogen, carbon monoxide, carbon dioxide and water, generally in the form of steam. On a smog basis the chief pollutants are unburned olefinic hydrocarbons and oxides of nitrogen.

The nuisance and health menacecreated by the exhaust gases of internal combustion engines have inspired the invention of many devices for their abatement. So far this problem has been attacked primarily by using combustion to consume unburned or partially burned hydrocarbons in the exhaust gas. Ingeneral two approaches have been used: (1) combustion in an after burner with auxiliary fuel at high temperature and (2) catalytic oxidation without auxiliary fuel. The first system has a major disadvantage in complexity and also in non-productive use of fuel. The second system has the disadvantage of employing an expensive catalyst demanding frequent catalyst regeneration. Moreover, the oxidation system generally operates at extremely high temperatures, thus requiring the use of heavy insulation to keepfrom ruining fioor carpets or rubber mats of automobiles. Neither of the systems otters a satisfactory method for substantially reducing the smog-causing constituents of exhaust gases.

It has now been found that air pollution can be advantageously controlled by passing exhaust gases and steam through a dual converter system. In accordance with the present invention the exhaust gases are first passed over a Group VIII metal-containing catalyst at a temperature of about 600 to 800 F., preferably about 650 to 750 F. at near-atmospheric pressure or slightly thereabove, and at a Weight hourly space velocity of about 0.5 to 20, preferably 0.5 to 5. In this first converter the carbon monoxide pollutant of the exhaust gas reacts with the steam in the exhaust gases to produce carbon dioxide and hydrogen. The hydrogen-containing efliuent from this converter is then passed over a hydrogenation catalyst at a temperature of about 400 to 700 F., preferably about 450 to 550 F., a pressure of about to 100 p.s.i.g., and a Weight hourly space velocity of about 0.1 to 3, preferably 0.1 to 1.5. In this second converter the hydrogen produced by the first converter saturates the olefinic pollutants and may slightly reduce the nitrogen oxide pollutants, primarily to ammonia and water.

In the first converter the steam shouldbe present in the exhaust gases in an amount in the range of about 2 to 20 volume percent, preferably about 3 to volume percent. The carbon monoxide content of the exhaust gases generally comprises about 1 to 20. volume percent, usually about 2 to 8 volume percent. The amount of carbon monoxide converted in the first converter will generally be equal to or greater than about 25 volume per cent, preferably equal to or greater than about 50 volume percent, of that present. The olefinic content in the exhaust gases will generally be equal to or less than about 8 volume percent, usually about 0.1 to 2 volume percent. The amount of olefins converted in the second converter will be equal to or greater than about volume percent, preferably equal to or greater than about 50 volume percent. The balance of the exhaust gases is made up' predominantly of nitrogen and nitrogen oxides which may at least in part be converted in the second reactor primarily toammonia and Water. Substantial amounts of carbon dioxide are also present. 7

The invention will be better understood by reference to the drawing which diagrammatically illustrates the process of the present invention.

The exhaust system 1 of an automobile internal combustion engine 3 is provided with first and second converters 5 and 7, respectively, in the form, for example, of catalytic mufflers. Steam for use in the process of the present invention is already present in considerable amount in the exhaust gases. If required an additional steam supply can be obtained by providing an auxiliary water reservoir similar to, for instance, that used for windshield wipers and employing the heat generated by the engine to convert the water into steam. This is shown diagrammatically in the drawing by water supply line 9 from a water reservoir (not shown) passing in heat exchange relationship with the engine 3. The steam produced thereby is conveyed to the exhaust system 1 by means of line 11. The exhaust gases and steam are passed into converter 5 and the eflluent from converter 5 then is to the atmosphere from converter 7. Converters 5 and 7 are containers that may take the general structural form of the well-known catalytic afterburners absent, of course, the provisions in these burners for an oxygen supply. See for example, Patents Nos. 2,909,415 and 2,828,- 189 to Houdry. The converters 5 and 7 are. each provided with a bed of catalyst that may be of uniform or irregular shape. 7

metal, for instance, the iron-transition group metals, iron,

cobalt, nickel; or a platinum group metal, e.g., platinum, palladium, rubidium and ruthenium, in the eiemental or hydrogenation catalysts such as tungsten, molybdenum,

vanadium, tin, chromium, the Group VIII metals, their oxides, sulfides or other combined, usually inorganic, form. Mixtures of these materials or compounds can be used and minor amounts of these catalytic ingredients may also be dispersed on or carried as promoters on suitable supports, for instance those noted above. The amounts of the catalytic metals on the carrier or support generally fall in the range of about 0.5 to 25 weight percent, preferably about 2 to 15 weight percent. Specific examples of suitable hydrogenation catalysts are cobalt-molybdenaon-alumina, nickel-tungsten oxide-on-alumina, nickel- Patented Feb. 23, 1965 The catalyst employed in converter 5 is a Group VIII tungsten sulfide-on-alumina, and cobalt-molybdena-onsilica-alumina.

Advantageously, the catalyst in converters 5 and 7 should be in pellet form. They should be relatively small in size and have smooth and rounded surfaces and preferably be of relatively uniform size and shape. Specifically, the pellets should have average dimensions of at least about ,4, and not greater than about A" to V2" and preferably from about to /s It is preferred that the bed of catalysts in the converters be in a relatively thin layer, that is, an arrangement in which the volume of the catalyst pellets necessary to effect the desired conversion is disposed in a layer whose thickness is small relative to the surface dimensions of the layer. This arrangement has the advantage of minimizing the back pressure imposed by the catalyst. This follows from the fact that pressure drop through a layer of catalyst pellets of given volume and with a given flow of exhaust gases is proportional approximately to the square of its thickness. The temperature conditions in these reactors are controlled by employing any proper insulation means and/or heat release device. Ordinarily the pressure required to effect the hydrogenation step of this process will naturally be present. Should the pressure he insufficient, however, low pressure exhaust gases can be compressed by means of power extracted from the drive shaft or engine.

The following example is included to further illustrate the present invention.

EXAMPLE I An automobile engine is run under average cruising conditions including an air flow of 112.5 lbs/hr. and a fuel flow of 10.0 lbs/hr. A sample of the engine exhaust is analyzed. The results of the analysis are shown in Table I.

The automobile exhaust system is equipped with converter 5 and converter 7 as diagrammatically shown in the drawing and the engine is run under the same conditions. Converter 5 contains iron oxide catalyst and converter 7 a platinum (2%) on alumina catalyst. The reaction conditions of the converters are shown in Table II.

T able II Converter 5 Convertcr 7 (Hz Pro- (Hydrogenaduction) tion) Temperature, F 700 500 Pressure, p.s.i.g 5 70 Weight hourly space velocity 1 2. 5 2 1.0

1 Based on C content only. 1 Based on olefin content only.

After the engine runs for a period of time, a sample of effluent is taken from converter and analyzed. The results are shown in Table III.

Table III Converter 5 Efilucnt (Aftcr H2 Production) Stock Wt. Lbs/hr. Percent Unburned Hydrocarbons:

Paraffins 0. 17 0.21 Olefin 0. l8 0. 59 C O 1. 33 1. 3 CO2 21. 72 26. 60 Stna m 4. 83 5. 92 Hz 0.20 0.25 O 0.22 0.27 N; and N Oxides 71. 05 87. 04

Table IV Converter 5 Efducnt (After Hydrogenation) Stock W t. Lbs./l1r. Percent Unburncd Hydrocarbons:

Paraflins 0. 58 0. 71 0. 10 0. 12

Comparison of the efiiuent composition from converter 7 (Table IV) and the composition of untreated exhaust gas (Table 1) illustrates the advantages of the present invention with respect to reducing the carbon monoxide and olefin contents of exhaust gases.

I claim:

1. A method of purifying exhaust gases consisting essential of carbon monoxide, nitrogen, oxides of nitrogen, olefinic hydrocarbons, steam and carbon dioxide which comprises passing the exhaust gases into contact with an iron oxide catalyst at a temperature of about 600 to 800 F. to convert at least about 25 volume percent of the carbon monoxide to carbon dioxide and produce hydrogen and passing the resulting hydrogen-containing effiuent into contact with a platinum catalyst at a temperature of about 400 to 700 F. to saturate at least about 25 volume percent of the olefinic constituents of the exhaust gas.

2. A method of purifying exhaust gases consisting essentially of carbon monoxide, nitrogen, oxides of nitrogen, olefinic hydrocarbons, steam and carbon dioxide, which comprises passing the exhaust gases into contact with an iron oxide catalyst at a temperature of about 600 to 800 F., and passing the resulting hydrogencontaining effluent into contact with a platinum catalyst at a temperature of about 400 to 700 F. to saturate olefinic constituents of the exhaust gas.

References Cited in the file of this patent UNITED STATES PATENTS 1,867,325 Neville July 12, 1932 1,919,626 Finn July 25, 1933 1,962,485 Dely June 12, 1934 OTHER REFERENCES Maxted: Catalytic Hydrogenation and Reduction," I & S Churchill, London, 1919, pages 28-31. 

1. A METHOD OF PURIFYING EXHAUST GASES CONSISTING ESSENTIAL OF CARBON MONOXIDE, NITROGEN, OXIDES OF NITROGEN, OLEFINIC HYDROCARBONS, STEAM AND CARBON DIOXIDE WHICH COMPRISES PASSING THE EXHAUST GASES INTO CONTACT WITH AN IRON OXIDE CATALYST AT A TEMPERATURE OF ABOUT 600 TO 800*F. TOCOVERT AT LEAST ABOUT 25 VOLUME PERCENT OF THE CARBON MONOXIDE TO CARBON DIOXIDE AND PRODUCE HYDROGEN ADN PASSING THE RESULTING HYDROGEN-CONTAINING EFFLUENT INTO CONTACT WITH A PLATINUM CATALYST AT A TEM- 